1. Field of the Invention
The invention is based on a method for converting energy from compressed air into mechanical rotary energy and an air motor driven by compressed air as generically defined by the preamble to claim 2, in particular for performing the method of claim 1.
2. Description of the Related Art
A compressed air motor with fluidically actuated rotary drive is known, in which energy from compressed air is converted into mechanical rotary energy in that a pivoting piston subjected to compressed air converts a reciprocating pivoting motion into a rotary motion of a power takeoff shaft, using a freewheel coupling between the pivoting piston and the power takeoff shaft; the advantages of an air motor over an electric motor are emphasized (DE G 93 20 601). The rotary motion generated by compressed air in this compressed air motor, however, is disadvantageously not continuous but instead is uneven, in accordance with the motion of the pivoting piston and the use of the freewheel coupling, depending on the rotary resistance. Another disadvantage of this known pivoting piston air motor is the expensive, complicated construction and the freewheel coupling that is also required, along with the comparatively high wear to the individual motor parts that is associated with it. Moreover, the production of such a compressed air motor is extraordinarily complex, making it correspondingly expensive.
Another known compressed-air-driven drive motor, although with a revolving rotor that actuates a power takeoff shaft, has vane cells that in the manner of a vane cell assembly are pressed by springs or centrifugal force radially against the wall, as is also known in manifold ways for air compressors (German Published, Unexamined Patent Application DE OS 31 17 412 A1). The disadvantage of this type of drive is that the sealing vanes, in the direction of the revolving shaft rotor, have a perpendicular surface contact with the housing wall along which they slide, with the disadvantage that it is extremely difficult to achieve low friction and corresponding tightness here, quite aside from the disadvantages of the extremely high production costs and the problems regarding wear from sealing and lubrication, which naturally has a direct effect on the service life or on the decreasing efficiency of the compressed air motor as the length of use increases. The compressed-air-driven drive motor in this reference is furthermore supposed to be used for compressed air tools, such as sanders, in which the actual driving quality is known to be far less critical than the service life.
In still another known compressed air motor (German Published, Unexamined Patent Application DE OS 196 13 262 A1), the rotary drive of the power takeoff shaft is effected via one of two shafts, coupled via a wheel gear, that carry two rotary pistons, which in a housing by subjection to compressed air are set contrarily into a rotary motion, similar to the reversal of a Roots blower in a compressed air motor. Once again, the problem above all is sealing and wear with the attendant lack of tightness after a certain time in operation, since in radial terms the two rotary pistons each run on walls of cylinder bores or the counterpart rotor and in the axial direction in turn run with the smooth end faces on correspondingly smooth end faces of the housing, and retroactive correction for sealing purposes after wear has occurred or changes in gaps have occurred from temperature changes is not possible. Although the housing wall and the rotary piston coating are supposed to be elastic in order to compensate for this known disadvantage, this nevertheless entails corresponding effort and expense. Once again, it has been thought of that a power tool, such as a drill spindle, be driven with this kind of rotary piston concentric motor. In each case, the elastic design of such rotary pistons is subject to stringent limits, since the rotary pistons rub on the housing wall rather than rolling on it, which in an elastic intermediate region leads to a severe braking action and considerable loss of rotary forces or of torque at the power takeoff shaft of the compressed air motor.
A primary problem of compressed air motors that convert the flow energy of the compressed air into rotary energy of a shaft is the quality of this conversion, namely the extent to which one kind of energy can be converted to the other with the least possible losses. In this case, the person skilled in the art has preferred vane cell pumps, because both friction an the internal tightness of the work chambers seemed easily controlled, and above all, these fundamental characteristics that are decisive for efficiency were already known by means of pumps of this type.
One skilled in the art would not have thought that a spur geared pump could serve as a compressed air motor, since the compressed air, in the way it attacks the work faces of the motor in the work chambers, would have a compensatory action. It is true that in the industry pneumatic motors have been indicated as a possibility (German Patent DE 42 41 320 C2), but in practice, they were not built. The reasons for this were also that the known compressed air motors either have fluctuations in the rotary drive, or the requisite torques do not appear sufficient. Still another motor based on a rotary piston has also been described (U.S. Pat. No. 3,856,440) with rotary pistons that have a spur toothing; the teeth have a cycloid development of the running face, so that motor action with a power takeoff task could occur. However, no thought was given to converting energy from compressed air into mechanical rotary energy for certain purposes, nor was it described before now, and because of the frequent presence of energy from compressed air, and above all also given the fundamental need for mechanical rotary energy, this was not obvious, either. In compressed air motors, which are a reversal of pumps and compressors, one skilled in the art thinks above all of rotating parts, whose surfaces acted upon by the driving medium have a lever action in the direction of rotation with respect to the axis of rotation, an example being a vane cell device. Usually, the fact that the next vane, following the driving vane and closing off the work chamber, generates a force that partially acts counter to the direction of rotation, is usually not thought of. This adverse effect with regard to the direction of rotation also exists in the first air motor mentioned (DE G 93 20 601). In that case there are only relatively slight fluctuations in the mechanical rotary energy generated, nevertheless, given the stringent demands at present for the uniformity of the rotation quality upon conversion into mechanical rotary energy, these fluctuations are unacceptable and disadvantageous, especially in the high rpm range, such as for dental equipment.